Pilot Director Lights (PDLs) generally consist of rows of lights mounted on the exterior of a refueling tanker aircraft for providing information to the pilot of an approaching aircraft to prepare for and maintain refueling boom engagement. Such lights may include lenses whose shapes or masking correspond to symbols or patterns to be illuminated to the approaching pilot.
PDLs are used for providing positional and operational feedback in order to help the approaching pilot prepare for and maintain contact between the refueling boom nozzle and a fuel receptacle of the receiving aircraft. For example, PDLs may provide information as to the elevational (vertical), telescoping (fore-aft) and lateral (azimuthal) position of the approaching aircraft relative to the refueling tanker. Also, PDLs may provide operational information to the receiving aircraft's pilot regarding, for example, the progress of the refueling process once the boom has been engaged.
FIG. 1 illustrates two light arrays used in conventional PDLs, which are mounted on a refueling tanker aircraft 10. Light array 22 is a row of lights that provide visual cues regarding the approaching aircraft's elevational position relative to an optimum position for refueling. The row of lights in light array 24 provides visual information regarding the approaching aircraft's fore-aft position relative to the optimum refueling point. As shown in FIG. 1, light array 22 is positioned on the port side of the tanker's fuselage, while light array 24 is mounted on the starboard side. Both arrays 22, 24 being located just forward of the leading edge of the wings.
FIG. 1 further shows that the symbols/patterns (arrows, rectangles, etc.) in light arrays 22 and 24 may illuminate at specific colors to provide positional information. For example, as the receiver aircraft approaches the refueling zone, the boom operator (aboard the tanker aircraft) may actuate signals through the PDLs to hold the receiver aircraft in the zone for the duration of the refueling operation. While in this zone, the lights indicate the progress of the operation along with signaling for any corrective maneuvers that the receiver pilot must perform to remain engaged with the refueling boom.
In conventional PDLs, such as those shown in FIG. 1, incandescent light bulbs may be used to illuminate the PDL symbols/patterns through tinted and diffused prismatic lenses. This results in various disadvantages. For example, the light being emitted from such PDLs may not be bright enough during daylight or fog conditions, due to losses incurred by the diffused and tinted lenses. Such losses also cause the PDLs to be very inefficient (normally less than 1% efficient). This requires the incandescent light sources in conventional PDLs to be operated at a high wattage, thereby generating much heat and reducing the operational life of the light sources.
Furthermore, conventional PDLs are not very redundant. For example, conventional PDLs may utilize two bulbs to illuminate the letter “D” of light array 22 in FIG. 1. It is possible, due to their short operational life, that one or both of these bulbs may burn out while the refueling tanker 10 is in the air, thus causing the “D” to be inadequately illuminated.
In addition, conventional PDLs, and even newer PDLs that use visible light emitting diodes (LEDs) as light sources are generally visible from a great distance at night. This is disadvantageous in situations where aircraft need to operate at night without detection by the unaided human eye.